The present applicant pertains to video surveillance systems, and more particularly to adjusting the focus of a surveillance camera.
Temperature changes cause thermal expansion of materials and thermal changes in the index of refraction of glass. Various cameras make adjustments to keep the lens in focus whether the focus is changing due to temperature changes, scene changes, vibration or other reasons, and some cameras can be set up to continuously adjust and maintain focus. However, this continuous adjustment can result in many long periods of focus hunting in the video. These focus shifts can result in blurry and out-of-focus video which can be objectionable to users. In addition, this method of operation requires mechanisms designed for many millions of cycles of focus adjustment because of the continuous adjustments to focus. Accordingly, there has been a need in the art for a method that minimizes the frequency of refocusing and does not require a mechanism to be designed requiring millions of cycles of operation.